Roof bolt connection



Nov. 18, 1969 G. w. ELDERS ROOF BOLT CONNECTION Filed Feb. 19, 1968 ATTORNEYS D W. ELDERS 3 v G R H m ma Mam FIG 2 L A L FIG. I

United States Patent 3,478,640 ROOF BOLT CONNECTION Gerald W. Elders, Hillcrest, Christopher, Ill. 62822 Filed Feb. 19, 1968, Ser. No. 706,583 Int. Cl. F16]: 13/04, 33/04 US. Cl. 85-64 11 Claims ABSTRACT OF THE DISCLOSURE A roof bolt connection having a wedge engaged with a spiral bolt-holding portion of a bolt, the wedge being relatively movable longitudinally of the bolt spirals. The wedge and bolt-holding portion provide a combined increased cross sectional dimension as the wedge moves relatively toward a bolt head, and engages the hole wall. The wedge and bolt-holding portion are urged into effective lateral compression with each other and with the hole wall upon relative turning of the bolt and wedge in one direction, whereby to secure the bolt in the roof. Upon relative turning in the opposite direction, the effective lateral compression is released, and the bolt and coacting wedge can be retrieved. Specifically, the spiral bolt-holding portion increases in cross section longitudinally toward the bolt head. The wedge has a spiral shape entwined with the spiral bolt-holding portion. The boltholding portion has a cross section, at the point on the bolt-holding portion of first effective lateral compression and longitudinally of such point toward the bolt head, at least as great as the minimum cross section of the bolt shank.

The method of forming the roof bolt includes the steps of placing an enlarged integral body on the shank end, making the body of a transverse circumference for a longitudinal distance from the integral juncture of the shank and body substantially greater than the transverse circumference of the shank, and then twisting the body into an extended spiral to form the bolt-holding portion in which the spiral has, for a predetermined longitudinal distance, a cross section at least as great as the minimum cross section of the shank.

Background of the invention This invention relates generally to a roof bolt connection and to the method of making a roof bolt.

Prior to the development of roof bolting, roof-falls were a continuous source of trouble to mine operators. Severe falls happened all too quickly, causing death or injury to workers, loss of production and high repair costs.

Roof bolting has provided an effective means of promoting safety in mine operations. The two general theories involved in roof bolting are (1) that the various layers of friable slate, shale, coal, etc., are suspended by bolts anchored in something more substantial overlying them; and (2) that the various bedded planes are bolted together to form a beam which prevents roof falls. In either case, sagging of the roof is prevented as the tension in each bolt tends to increase the friction between the layers, thus minimizing horizontal pressures.

Roof bolts have other obvious advantages. Because timbers are unnecessary, ventilation is improved, and greater freedom for operating mechanized equipment is provided. Fire hazards are also eliminated, since there is no need to store quantities of flammable material, I

cooperation with a wedge plug inserted in the hole, the shell cannot be retrieved, and if it could be retrieved, it is certainly not reusable. In most instances, the bolt and the wedge plug cannot be retrieved or reused either.

Summary of the invention The present roof bolt connection enables both the bolt and a coacting, lateral compression wedge to be retrieved and reused, if desired, thereby reducing the costs of roof bolting considerably. The roof bolt and coacting wedge are simple in construction, economical to manufacture, and highly efficient in operation.

The bolt includes a spiral bolt-holding portion and a coacting wedge engageable with and movable longitudinally of the bolt-holding portion. As the wedge moves relatively toward the bolt head, upon relative rotation in one direction, the wedge and bolt-holding portion provide a combined increased cross sectional dimension so that the wedge and bolt-holding portion are urged into effective lateral compression with each other and with the hole wall, whereby to secure the bolt in the roof under tension.

Upon rotation of the bolt in the opposite direction, the combined cross sectional dimension of the wedge and bolt-holding portion is decreased as the wedge moves relatively away from the bolt head, whereby to release the lateral compression and to retrieve both the wedge and bolt.

The spiral bolt-holding portion increases progressively in cross section longitudinally in the direction toward the bolt head, and thereby increases progressively the combined cross sectional dimension of the wedge and bolt-holding portion in order to achieve effective securement of the wedge and bolt-holding portion at a fixed location in the hole. When the wedge is fixed, the interengagement of the wedge and spiral bolt-holding portion causes the bolt to move into the hole and causes the bolt to be placed under tension upon continued rotation of the bolt.

The wedge has a spiral shape and is entwined with the spiral bolt-holding portion for controlled longitudinal relative movement in either direction upon selective bolt rotation.

The spiral bolt-holding portion has a developed circumference greater than the hole diameter, at a location between the point of effective lateral compression and the bolt shank, which turns into the hole wall upon bolt rotation and provides a frictional resistance that augments the load capability provided by the cross section of the bolt-holding portion in opposition to tension applied to the bolt.

The method of forming the roof bolt comprises the steps of placing an enlarged integral body on the shank end, making the body of a transverse circumference substantially greater than the transverse circumference of the shank for a longitudinal distance from the integral junc ture of shank and body, and then twisting the body into an extended spiral to provide the bolt-holding portion, the cross section of the bolt-holding portion being greater than the shank cross section for a distance longitudinally from such juncture.

Brief description of the drawing FIG. 1 is an elevational view of the roof bolt before final formation;

FIG. 2 is an elevational view of the formed roof bolt;

FIG. 3 is an elevational View of the roof bolt connection in a roof, the wedge being shown in broken lines to indicate a position prior to effective lateral compression and being shown in full lines to indicate a position at which effective lateral compression is attained;

3 FIG. 4 is a cross section taken on line 4--4 of FIG. 3, and

FIG. 5 is a cross section taken on line 55 of FIG. 3.

Description of the preferred embodiment Referring now by characters of reference to the drawing, and first to FIGS. 1 and 2, the structure and formation of a roof bolt generally indicated by Will be described. The bolt 10 includes an elongate shank 11 having a bolt head 12 attached at one end. Formed integrally with the other end of the shank 11 is an enlarged body 13. Considered relative to the longitudinal bolt axis, the body 13 enlarges or swells laterally and outwardly from the juncture 14 of the shank 11 and body 13, reaching a maximum transverse circumference, and then diminishing in circumferential size to its end. With this structure, it will be understood that the transverse circumference of the body 13 is substantially greater than the transverse circumference of shank 11 for a longitudinal distance from the integral juncture 14 of the shank 11 and body 13.

Then, the body 13 is twisted and pulled into an extended spiral to provide the bolt-holding portion 15, best shown in FIG. 2. Because of the particular enlarged arrowhead-shaped of body 13 prior to the spiral formation of the bolt-holding portion 15, the bolt-holding portion 15 has a cross section for a considerable longitudinal distance from the juncture 14 which is greater than, or at least as great as, the minimum cr oss section of the bolt shank 11. For reasons which will later appear, the cross section of the spiral bolt-holding portion 15 increases progressively from its outer end in a direction toward the bolt head 12. Moreover, the developed longitudinal circumferential configuration of the spiral boltholding portion is tapered from the juncture 14 to the outer end.

From FIG. 3 it is seen that the roof 16 is provided with a longitudinal hole 17, defined by a hole wall 20, of a predetermined diameter. The greatest diameter of the tapered, developed circumferential configuration of the bolt-holding portion 15 is greater than the diameter of hole 17 so that at least a portion of the spiral of the boltholding portion turns into the hole wall 20 upon insertion of the bolt 10 into the hole 17 and upon rotation of the bolt, whereby to provide a frictional resistance to bolt withdrawal.

A coacting wedge 21 is used in association with the bolt 10. The wedge 21 engages the bolt-holding portion 15 and is relatively movable longitudinally along the spirals. Specifically, the wedge 21 is of a spiral shape and is entwined with the spiral bolt-holding portion 15 for relative movement longitudinally of the bolt 10 upon bolt rotation.

When the bolt 10 and coacting wedge 21 are inserted into the hole 17, the wedge 21 is placed in entwined engagement with the end of the spiral body portion 15 having the smaller cross section. As the bolt 10 is turned in one direction, the wedge 21 will move spirally, longitudinally down along the bolt-holding portion 15 until the wedge 21 comes into effective lateral contact with the hole wall 20. The wedge 21 is shown in broken lines in FIG. 3 to indicate the position of the wedge 21 before its final location shown in full'lines.

Because the spiral bolt-holding portion 15 increases in cross section longitudinally in the direction toward the bolt head 12, the combined cross sectional dimension of the wedge 21 and the bolt-holding portion 15 increases progressively as the wedge 21 moves relatively toward the bolt head 12 upon bolt rotation in one direction. When the combined cross sectional dimension of the wedge 21 and bolt-holding portion 15 equals or exceeds the diameter of hole 17, the wedge is in effective lateral contact with the hole wall 20, and the position of the wedge 21 is fixed. Upon continued rotation of the bolt 10 in the same direction, the bolt-holding portion 15 moves 4 upwardly into the hole 17 past the wedge 21, all the while progressively increasing the combined cross sectional dimension of the wedge 21 and bolt-holding portion 15, thereby urging the wedge 21 and bolt-holding portion 15 into effective lateral compression with each other and with the hole wall 20 to secure the bolt 10 in the roof 16.

It will be importantly noted that both the wedge 21 and the bolt-holding portion 15 are in effective lateral compression with the hole wall 20. The entire longitudinal length of the wedge 21 is such engagement, and the corresponding longitudinal spiral length of body-holding portion 15 cooperating with the wedge 21 is also in such effective compression with hole wall 20. The wedge 21 and the cooperating spiral length provide effective lateral compression with hole wall 20 completely around the circumference of the hole wall 20.

A comparison of FIGS. 4 and 5 discloses the increasing combined cross sectional dimension of the wedge 21 and bolt-holding portion 15. FIG. 4 shows a combined cross sectional dimension that is not sufficiently great enough for the wedge 21 to be in effective contact with the hole wall 20. FIG. 5 discloses that the cross section of the spiral bolt-holding portion 15 has increased sufficiently so that the combined cross sectional dimension is greater than the diameter of the hole 17, thereby causing effective lateral compression between the wedge 21 and bolt-holding portion 15, and between these parts and the hole wall 20.

In assembly, a plate 22 is usually clamped by the bolt 10 against the roof 16. When the bolt 10 is turned further to tighten the bolt 10', the spiral interengagement of the Wedge 21 and bolt-holding portion 15 places the bolt 10 under tension as the bolt-holding portion 15 moves past the wedge 21 and as the bolt head 12 engages the plate 22. The effective lateral compression between the wedge 21 and the bolt-holding portion 15 secures the bolt 10 in place and prevents unintentional withdrawal of the bolt 10 from the hole 17.

It will be understood that the bolt-holding portion 15 has a cross section, at the point on the bolt-holding portion of first effective lateral compression between the wedge 21, bolt-holding portion 15 and hole Wall 20 and longitudinally from such point in a direction toward the bolt head 12, at least as great as the minimum cross section of the bolt shank 11. With this structural arrangement, any failure of the bolt 10 attributed to the tension placed on the bolt 10 will be determined by the cross sectional area of the bolt shank 11. Consequently, the ultimate load of the bolt 10 can be controlled by a predetermined shank diameter.

Under some circumstances, it is possible for the cross section of the bolt-holding portion 15 at the point of effective lateral compression to be less than the cross section of bolt shank 11. For example, the largest, developed circumference of the bolt-holding portion just beyond the juncture 14 is slightly greater than the diameter of hole 17. Therefore, as the bolt 10 is turned, the spiral length of the body-holding portion 15 having this enlarged circumference, is compressed and turned into the hole wall 20. This interengagement provides a frictional resistance that augments the load capability provided by the cross section of the bolt-holding portion 15 in opposition to the tension applied to the bolt 10. By appropriate design of the cross section of the spiral bolt-holding portion 15, and of the frictional resistance of the spiral length of the bolt-holding portion 15 with the hole wall 20 longitudinally of the point of effective lateral compression in the direction toward the bolt head 12, the ultimate load of the bolt 10 under tension can be accommodated.

With this roof bolt connection, both the bolt 10 and the wedge 21 can be retrieved for subsequent replacement and usage in the same or a different roof hole 17. Upon turning the bolt 10 in the opposite direction from that previously described, the bolt 10 moves in a direction toward the hole opening and the bolt-holding portion 15 moves past the fixed wedge 21. Because of the progressively decreasing cross section longitudinally of the tapered bolt-holding portion 15, the combined cross sectional dimension of the wedge 21 and bolt-holding portion 15 is similarly progressively decreased. At some point of such relative movement of wedge 21 and bolt-holding portion 15, the combined cross sectional dimension will be less than the diameter of hole 17, and consequently, the effective lateral compression between the wedge 21 and bolt-holding portion 15 and between such parts and the hole wall 20, is elfectively released. The bolt 10 and the wedge 21 can then be withdrawn from the hole 17.

It is thought that the functional advantages of the roof bolt connection and the method of making such roof bolts have become fully apparent from the foregoing detailed description of parts, but for completeness of disclosure, the installation of the roof bolt connection will be briefly described.

First, a hole 17 is bored into the roof 16, the core having a predetermined diameter. Then, the bolt 10 is inserted through the plate 22, and the bolt shank 11 and bolt-holding portion 15 are placed and turned into the hole 17 with the coacting wedge 21 entwined with the small tapered end of the bolt-holding portion 15. As the bolt 10 is turned in one direction, the wedge 21 will move relatively and spirally, longitudinally along the spiral bolt-holding portion 15 until the combined cross sectional dimension of the wedge 21 and bolt-holding portion 15 is sufiicient to provide an eifective lateral compression with each other and with the hole wall 20. At this point, the wedge 21 becomes fixed in position in the hole 17, and upon continued turning of the bolt 10 in the same direction, the spiral bolt-holding portion 15 will move upwardly past the wedge 21. Because the cross section of the spiral bolt-holding portion 15 progressively increases, the combined cross sectional dimension of the wedge 21 and bolt-holding portion 15 progressively increases, thereby increasing the efiective lateral compression and effectively binding the bolt 10 in the roof 16. As the bolt 10 is turned up tight, so that the bolt head 12 clamps the plate 22 to the roof 16, the bolt shank 11 and that length of the bolt-holding portion 15, in a direction toward the bolt head 12 from the location of effective lateral compression, is under tension. Because the bolt shank 11 is of a predetermined diameter, and is of the smallest cross section under tension, the bolt 10 can be readily designed for a predetermined load. The bolt 10 is now installed.

The bolt 10 and the coacting wedge 21 can be readily retrieved, if needed. Simply turning the bolt 10 in the opposite direction unwinds the spiral bolt-holding portion 15 past the wedge 21 until the combined cross sectional dimension of the wedge 21 and bolt-holding portion 15 is diminished to an extent so as to release the effective lateral compression between such parts and the hole wall 20. Then, both the bolt 10 and the coacting wedge 21 can be simply removed from the roof hole 17. The bolt 10 and the coacting wedge 21 can be reinserted in the same hole or can be installed in another compatible hole. With this roof bolt connection, both the bolt 10 and the wedge 21 are retrievable and reusable.

I claim as my invention:

1. A roof bolt connection, comprising:

(a) a bolt having a central axis including:

(1) a head,

(2) a shank extending from the head, and

(3) a bolt-holding portion extending integrally from the shank, the bolt-holding portion, lying on a spiral, the spiral aXis of which is entwined about but offset from the central axis,

(b) a coacting wedge engaged with the spiral boltholding portion, the wedge being of a lesser length than the bolt-holding portion and relatively movable 6 longitudinally of the central axis on the bolt-holding portion, and

(c) the wedge and bolt-holding portion providing a combined increased cross sectional dimension as the wedge moves relatively toward the bolt head.

2. A roof bolt connection, as defined in claim 1, in

which:

' (d) the spiral bolt-holding portion increases in cross section longitudinally in the direction toward the =bolthead.

3. A roof bolt connection as defined in claim 1, in

which:

((1) the wedge has a spiral shape and is entwined with the spiral bolt-holding portion, the wedge being relatively movable along the spirals of the boltholding portion upon relative turning of the bolt and wedge.

4. A roof bolt connection as defined in claim 1, in

which:

((1) the bolt-holding portion has a developed, longitudinal circumferential configuration tapered in a direction away from the bolt head,

(e) the spiral bolt-holding portion increases substantially progressively in cross section longitudinally in a direction toward the bolt head, and

(f) the wedge has a spiral shape and is entwined with the spiral bolt-holding portion.

5. A roof bolt connection in a roof having a longitudinal hole of a predetermined diameter, comprising:

(a) a bolt having a central axis including:

(1) ahead,

(2) a shank extending from the head, and

(3) a bolt-holding portion extending integrally from the shank, the bolt-holding portion lying on a spiral, the spiral axis of which is entwined about but offset from the central axis of the shank,

(b) a coacting wedge engaged with the bolt-holding portion, the wedge being of a lesser length than the bolt-holding portion and relatively movable longitudinally of the central axis on the bolt-holding portion,

(c) the wedge and bolt-holding portion providing a combined increased cross sectional dimension as the wedge moves relatively toward the bolt head, and engaging the wall of the hole, and

(d) the wedge and bolt-holding portion being urged into efiective lateral compression with each other and with the roof upon relative turning of the bolt and wedge, whereby to secure the bolt in the roof.

6. A roof bolt connection as defined in claim 5, in

which:

(e) the spiral bolt-holding portion increases in cross section longitudinally in the direction toward the bolt head, thereby increasing the combined cross sectional dimension of the wedge and bolt-holding portion as the wedge moves relatively toward the bolt head upon bolt rotation in one direction in order to achieve effective securement of the wedge and bolt-holding portion at a fixed location in the hole.

7. A roof bolt connection as defined in claim 5, in

which:

(e) the combined cross sectional dimension of the wedge and bolt-holding portion is decreased as the wedge moves relatively away from the bolt head upon bolt rotation in the opposite direction, whereby to release the efiective lateral compression between the wedge, bolt-holding portion and roof, and to retrieve both the wedge and bolt.

8. A roof bolt connection as defined in claim 5, in

which:

(e) the wedge has a spiral shape and is entwined with the spiral bolt-holding portion for relative movement longitudinally of the bolt upon bolt rotation.

9. A roof bolt connection as defined in claim 5, in which:

(e) the bolt-holding portion has a cross section, at

the point on the bolt-holding portion of first effective lateral compression between the Wedge, boltholding portion and roof and longitudinally from such point in a direction toward the bolt head, at least as great as the minimum cross section of the bolt shank.

10. A roof bolt connection as defined in claim 9, in 10 which:

(f) the bolt-holding portion has a developed circumference greater than the hole diameter, at a location between the point of effective lateral comupon bolt rotation in the opposite direction, whereby to release the efiective lateral compression, between the wedge, bolt-holding portion and roof, and to retrieve both the wedge and bolt.

pression and the bolt shank, which turns into the References Cited wall upon bOlt rotation and provides frictional 1'6- UNITED STATES PATENTS sistance augmenting the load capability provided 1618 239 2/1927 Ta lor 85-2O t th -h d o i y by cross sec 108 of e bolt 01 1n portion in op- 3391720 7/1968 Morse 151 14 position to tension applied to the bolt.

11. A roof bolt connection as defined in claim 5, in FOREIGN PATENTS which:

(e) the bolt-holding portion has a longitudinal, de-

veloped circumferential configuration tapered in a 21852 11/1905 Great Briiain direction away from the bolt head, 809987 3/1959 Great Britain' (f) the spiral bolt-holding portion increases in cross 25 853206 11/1960 Great Britain' section longitudinally in the direction toward the bolt head, thereby increasing the combined cross sectional dimension of the wedge and bolt-holding portion as the wedge moves relatively toward the bolt head upon bolt rotation in one direction in order to achieve effective securement of the wedge MARION PARSONS, JR., Primary Examiner US. Cl. X.R. -79 

